[quote name='Dan Dare' timestamp='1478797810' post='3171744']
Do you mean a trill (swiftly varying between two adjacent notes a semitone apart) or actual vibrato (where pitch usually varies by a lot less than a semitone)? If you're talking about a trill, strike the note and hammer on and off (either a fret up or a fret down) swiftly. There's a limit to how long it will sustain, but it works. It's very tricky to slide between two fretted notes - buzz is almost inevitable as you cross the fret and the pressure on the string is released momentarily. Applies especially if you use roundwounds. Vibrato much easier on a fretless - you mention Sting. He plays fretless and would, I suspect, use one for a song that demands vibrato.
[/quote] I think Dan when he says Sting, it's a term for a trill/vibrato etc. Yeah i had never heard of it either.